Field of the Invention
The present invention relates to a dock for portable devices, and, in particular, to a Universal Serial Bus (USB) dock capable of charging a portable device in response to the detected operating state of the portable device.
Description of the Related Art
The demand for new features and the ability to easily connect peripheral devices to computer systems has led to several new developments in computer systems in recent years. One such development is the Universal Serial Bus (USB). The USB specification was developed in order to provide an external expansion bus which allowed peripheral devices to be added with the same ease as connecting a telephone to a wall jack. Since its introduction, USB has enjoyed widespread acceptance in the marketplace.
USB On-the-go (OTG) defines two roles of devices: OTG A-device and OTG B-device. This terminology defines which side supplies power to the link, and which is initially the host. The OTG A-device is a power supplier, and an OTG B-device is a power consumer. The default link configuration is that the A-device acts as USB Host and the B-device is a USB peripheral. USB On-The-Go introduces the concept that a device can perform both the master and slave roles, and so subtly changes the terminology. With OTG, a device can be either a host when acting as the link master, or a peripheral when acting as the link slave. The choice of whether to be host or peripheral is handled entirely by which end of the cable the device is plugged into. The device connected to the “A” end of the cable at start-up, known as the “A-device”, acts as the default host, while the “B” end acts as the default peripheral, known as the “B-device”.
In the USB battery charging specification, USB devices always draw power from USB hosts. If the user wants to use his portable device as a USB host, a specific type of cable having an ID pin is usually used. In this regard, a USB micro A/B cable having an OTG ID pin is usually used. When a USB device is connected to a portable device via the USB micro A/B cable, the portable device will switch from the USB device mode to a USB OTG host mode, and the portable device may provide power to the connected USB device.
In a docking scenario, the user may be stationary for a long period of time, and generally requires the use of a large-screen and traditional input devices such as a keyboard or a mouse. USB docks can provide the required video and USB input/storage functionality while the portable device is in the USB OTG host mode. However, the portable device is utilizing its own power while in the USB OTG host mode. Even if the USB dock has its own power source, the power of the USB dock cannot be shared with the portable device because the function is not defined in the USB battery charging specification.